The invention relates to tow bar constructions for commercial vehicles, more particularly trucks, trailers, and their tractors, which may commonly be called transport vehicles. Axle assemblies found in these vehicles have been described e.g. in Finnish Patents 84,895 and 89,570. The invention further relates to transport vehicle combinations some of which comprise axle and/or tandem axle assemblies of the type described above.
Steerable rigid axles are used in special heavy transports, in which one or more axles have to be steered since they typically number more than two, and since the wheel turning radius of the vehicle is insufficient without steering. Rigid axles are used because of the heavy load and the simple structure. It is also crucial that the load be distributed evenly on all axles in rough terrain, in that the travel direction of the wheels is at all times towards their direction of rotation in curves and when travelling straight ahead.
Twin wheels with independent suspension have generally been used, the construction meeting the requirements set on turning and load distribution.
Axles fixedly journalled to the chassis by means of a turntable can also be used. The requirements set on turning are met, but not those set on load distribution when there are several axles, since the axles have not been coupled together in the turntable construction. Nor is the requirement that the wheels move in their direction of rotation met if several axles are supported by the turntable, or if several axles are directly suspended on the chassis. In this case the resistance to motion of the transport vehicle becomes high in curves, the stress in its structural members increases and tire wear and energy consumption increase in curves as compared with travel on a straight road.
Also known are various solutions for evening out the load by the use of a plurality of trailers. The drawback here is that the transport combinations are difficult to handle.
It is also known to use wheels with independent suspension, each wheel having its own turntable, so that the wheels easily turn even 180 degrees. In this case the wheels are often steered using electronics and hydraulics. The solution is complex and expensive, and demanding as regards maintenance.
Solutions are also known from Finnish patents 84,895 and 89,570. In these solutions the turning of the axles is provided by affecting the positions of the longitudinal supports of the axle assembly and the suspension bars of the springs, and they very well meet the requirements set on control of axle turning, load distribution on different axles, wheel movement in the direction of rotation, and co-operation of successive axles in multi-axle tandem axle assemblies.
Solutions are also known from Finnish patent application 954,662. In these solutions compensation for the lifting action of the chassis and mechanical control of the axle carrying members of the transport vehicle are achieved when the axles are turned. These features have certain positive effects on the operation of the transport vehicle.
As was mentioned above, a tow bar construction between a tractor and a trailer, or between tractors or trailers has not been described in the above publications. Utilizing a tow bar for steering a tractor and a trailer, and tractors and trailers, would be structurally advantageous and flexible in use.
It is an object of the present invention to provide solutions for using a tow bar in steering the axles of a trailer or a corresponding transport vehicle.
In the present invention, steering is effected mechanically by the action of the tow bar turning angle in a plane parallel to the surface of the road, the angle being formed in curves relative to the tow bar and the chassis of the trailer. Although the steering force is mechanically transmitted directly to all trailer axles intended to be turned, it is also possible to use e.g. a hydraulic servo. The turntable commonly used in trailers is replaced by e.g. an axle suspension according to Finnish patents 84,895 and 89,570.
The construction of the invention allows the turning of one or more axle assemblies in a trailer, whereby also the following essential requirements are met: load compensation between axles, wheel movement to their direction of rotation in curves, trailer follows tractor travel track in curves, reduced energy consumption and e.g. tire wear in curves, and a lesser general stress on the construction elements.
The manner of steering in accordance with the invention also allows several successive trailers to be connected and steered as described above, steering power and steering geometry being transmitted to each trailer from the tow bar and the preceding trailer. It is also possible to couple together several motorized vehicles or couple together motorized and non-motorized transport vehicles arbitrarily as will be described below.
There may be one or more axles steered by the tow bar, and even non-steerable axles may be included in the transport vehicle. At least the following alternative arrangements may be listed incorporatedable subject invention:
one steering axle and one or more fixed axles PA1 two steering axles and one or more fixed axles PA1 three steering axles and one or more fixed axles PA1 four steering axles and one or more fixed axles PA1 two steering axles PA1 three steering axles PA1 four steering axles.
Even other combinations can be implemented with the tow bar construction of the invention.
In the following the invention will be described in more detail by means of examples of some embodiments with reference to the attached drawings.